Endoscopes of the present type are generally known with both rigid and flexible designs and are used not only for examining cavities, for instance in motors and turbines, but also in medicine for diagnostic or therapeutic purposes. Since endoscopes in operation are frequently used in cavities filled with often aggressive fluids or in cavities with high humidity, it is necessary for the distal end window to close the outer tube, in which the endoscope's optical system is disposed, in a fluid- and gas-tight manner.
Stringent demands are made on this fluid-and gas-tight juncture of the end window to the outer tube, since the outer tube with the end window can not only be located in aggressive media, but it can also be exposed to high temperatures. Especially in the case of medical endoscopes the connection of the end window to the outer tube is subjected to severe stress by being placed in a sterilizing solution and/or by being sterilized by hot steam at approximately 140.degree. C. in an autoclave. The proximal eyepiece window undergoes the same hard treatment as the distal end window during the sterilization procedure.
In most known endoscopes the end windows are glued into the outer tube or the eyepiece cup. However, experience has shown that adhesions age and become leaky particularly when exposed to fluctuating temperatures and additionally to aggressive media. After a certain operating time moisture and/or fluids can penetrate into the endoscope.
For this reason, a proposal according to DE 37 40 417 A1 is to mount a metallic film on the peripheral surface of the distal end window and to solder this metallic film to the outer tube, which generally consists of a noncorrosive metal.
A so-called "close-joint soldering" is required for this. However, it is very difficult to check for faults, etc. in the soldering layer created in a close-joint soldering process. For this reason, in serial production it is possible to overlook faults in the joint, the result of this being that after a certain time the end window of the endoscope no longer has a fluid-tight seal.